In the prior art, a number of techniques have been developed for treating occluded blood vessels. One type of treatment is to surgically attach unblocked vessels to bypass the occlusion. Another surgical approach is to remove the occlusion from within the vessel. More recently, dilatation catheter devices have been developed which can be inserted into the blood vessel having an occlusion.
One type of dilatation catheter can be found in U.S. Pat. No. 4,271,839, issued June 9, 1981, and assigned to the same assignee as the subject invention. In this device, an elastic balloon element is sealingly attached to the distal end of a catheter. The balloon element is held in an inverted condition within the catheter. In use, the catheter is brought into position adjacent the occlusion. The balloon element is everted from the catheter through the occlusion by applying fluid pressure to the interior of the catheter. The balloon is extruded through the occlusion in anisotropic fashion, that is, in advance of substantial lateral expansion of the balloon. Once the balloon is in place within the occluded section of the vessel, continued fluid pressure is applied to laterally expand the balloon and dilate the occlusion. When the occlusion has been treated, the fluid pressure is released causing the balloon to collapse. A cord connected to the free end of the balloon is then retracted to reinvert the balloon within the catheter prior to removal of the catheter from the blood vessel.
The particular dilatation catheter discussed above has many important advantages. For example, it has been found to be highly beneficial to have a balloon member in an initially inverted condition and to extrude that balloon member through the occlusion. This linear rolling extrusion method produces very little friction between the balloon member and the occluded vessel wall. The catheter of the subject disclosure is intended to provide the advantages of the catheter described in U.S. Pat. No. 4,271,838, and to provide additional improvements thereto as discussed below.
As pointed out above, prior art inverted balloon dilatation catheters have extruded the balloon member used therein under fluid pressure. In use, the balloon member tends to advance with initial, abrupt and uncontrolled motions. Relatively high pressures are required to begin the extrusion process when the balloon is completely inverted. As the balloon begins the eversion process, lower pressures are required. The requirement to change the pressure occurs quite rapidly and is therefore difficult for the catheter operator to adjust.
Another difficulty with the prior art dilatation catheters concerns the different pressure requirements needed to extrude the balloon member through a stenosis and the dilation process itself. The pressure required to overcome the frictional forces between the balloon member and the catheter during the extrusion process is quite high compared to the pressures required for the dilation process and assumes a significant portion of the total inflation pressure. It would be desirable to reduce the amount of fluid pressure needed to extrude the balloon, reserving that pressure more for dilation.
As discussed above, in prior art evertable catheters, means is provided for reinverting the balloon member prior to retraction of the catheter from the blood vessel. It was found desirable to reinvert the balloon member to reduce friction between the balloon member and the blood vessel wall during retraction. It is also desirable in that it enables the balloon element to be used for the serial treatment of multiple occlusions within a vessel, with reinversion occurring before each serial dilation. Because the balloon member is sometimes quite long compared to the diameter of the catheter, folds of the depressurized elastic balloon member often became bunched up around the mouth of the catheter during the reinversion process. The cluster of folds at the end of the catheter can actually result in an increase in the effective diameter of the catheter and thereby increase friction. Accordingly, it would be desirable to provide a catheter which reduces the likelihood of the balloon bunching up near the distal end of the catheter during reinversion.
Accordingly, it is an object of the subject invention to provide a new and improved method and apparatus for dilating occluded blood vessels.
It is another object of the subject invention to provide a new and improved method for manually extruding a balloon element into a body passage.
It is a further object of the subject invention to provide a new and improved method for combining a manual technique with a pressurized eversion to extrude a balloon member.
It is another object of the subject invention to provide a new and improved method of reinverting a balloon member without bunching.
It is still a further object of the subject invention to provide an improved new and improved apparatus for extruding a balloon member into a body passage.
It is still another object of the subject invention to provide a catheter which can extrude a balloon member in a gentle, even manner, avoiding abrupt movements.
It is still a further object of the subject invention to provide a new and improved catheter having enhanced dilation capabilities.
It is still another object of the subject invention to provide a new and improved catheter where the difference between the pressure required to extrude the balloon and and the pressure required to produce dilation is reduced thereby reducing the chance of balloon breakage.